Quiet rotor blade and wind energy installation equipped with rotor blades of this type

ABSTRACT

The invention concerns a rotor blade and a wind power installation having a rotor blade provided with a rotor blade trailing edge, wherein the rotor blade tapers towards the rotor blade trailing edge. The invention is distinguished in that, in the region of the rotor blade trailing edge, the degree of taper of the rotor blade increases in a direction towards the rotor blade trailing edge, and there is no stair-like step in the rotor blade at least in the region of the rotor blade.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a §371 of PCT/EP98/05615, filed Sep. 4, 1998.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH OR DEVELOPMENT

NOT APPLICABLE

REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAMLISTING APPENDIX SUBMITTED ON A COMPACT DISK.

NOT APPLICABLE

BACKGROUND OF THE INVENTION

The invention concerns a rotor blade and a wind power installationhaving a rotor blade, wherein the rotor blade is provided with a rotorblade trailing edge and tapers towards the rotor blade trailing edge.

Rotor blades for wind power installations are known in many differentforms. Unfortunately many rotor blades in the state of the art sufferfrom the problem that in operation of the wind power installation andwith wind strengths from about 5 to 6 m/second, they generate notinconsiderable sound emissions, to a not inconsiderable extent. Thesound emissions which have occurred hitherto mean inter alia that windpower installations meet resistance on the part of wide classes ofsociety and population, because of the amount of noise generated. As aconsequence, wind power installations sometimes encounter difficulty inbeing accepted or are not accepted at all, as the authorities withresponsibility for granting permission for setting up wind powerinstallations refuse such permission because of the environmentalconsiderations involved—noise also counts as environmental pollution.Therefore, for reasons of noise, particularly in the proximity ofresidential buildings, it is desirable to reduce the above-mentionedconsiderable levels of noise emission, in order to satisfy the statutoryrequirements and to increase the acceptance of wind power installations.

Therefore the object of the present invention is to reduce the level ofsound emissions of wind power installations.

BRIEF SUMMARY OF THE INVENTION

In accordance with the invention, with a rotor blade of the kind setforth in the opening part of this specification, that object is achievedin that in the region of the rotor blade trailing edge the degree oftaper of the rotor blade increases in a direction towards the rotorblade trailing edge, and there is no stair-like step in the rotor bladeat least in that region of the rotor blade.

A particularly advantageous embodiment of the invention is distinguishedin that the degree of taper of the rotor blade increases at givenspacings in a direction towards the rotor blade trailing edge. In thatrespect, it is particularly preferable that bends in the cross-sectionof the trailing edge portion of the rotor blade, that is to say aportion adjacent to the rotor blade trailing edge, are formed at therespective spacings, and between said bends said portion of the rotorblade is substantially flat. Then, in this form of the invention, theplanes which are disposed between the bends form very shallow anglesrelative to each other so that overall the assembly gives approximatelythe form of a convexly curved surface in respect of the cross-section ofthe trailing edge portion of the rotor blade.

In a further advantageous embodiment of the rotor blade according to theinvention, there are three bends each extending substantially parallelto the rotor blade trailing edge. That embodiment represents an optimumcompromise between the expenditure involved in production of the bendsin the rotor blade, and a desired marked reduction in the noise level ofthe rotor blade as it moves.

It is particularly preferred that the inclined planes which adjoin eachother in the form of bends and which form the taper configuration forthe rotor blade in a direction towards the rotor blade trailing edge areprovided only on one side of the rotor blade. In that case it isadvantageous if the bends are formed only on the suction orreduced-pressure side of a rotor blade having a pressure side and areduced-pressure side. That configuration provides for a particularlymarked reduction in the level of sound emissions. In that case, it hasproven to be desirable that the acute angles which the planes of thereduced-pressure side of the rotor blade, that are between the bends,form with the pressure side of the rotor blade, become increasingly moreacute. In that respect, the reduction in the magnitude of the respectiveangles occurs from the trailing edge towards the leading edge of therotor blade. The plane portion of the reduced-pressure side of the rotorblade, which is most closely adjacent to the rotor blade trailing edge,then forms the almost sharp rotor blade trailing edge, with the flatpressure side of the rotor blade.

Wind power installations provided with the rotor blade according to theinvention overall exhibit a marked reduction in the noise levelgenerated, by virtue of the reduced sound emission of the individualrotor blade. Accordingly, the wind power installations according to theinvention represent a markedly reduced noise pollution aspect for thepopulation. Therefore, the wind power installation according to theinvention considerably reduces the above-discussed disadvantages of thewind power installations in the state of the art, the level ofacceptance of wind power installations on the part of the people isincreased and existing anti-noise requirements are more easily met.

Further advantageous embodiments of the invention are set forth in theappendant claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in greater detail hereinafter by means of anembodiment illustrated in the accompanying drawing. In the drawing:

FIG. 1 is a view in cross-section through a rear portion, which istowards the rotor blade trailing edge, of an embodiment of the rotorblade according to the invention, and

FIG. 2 shows a portion from FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, shown therein is an embodiment of a rotor blade 1according to the invention. FIG. 1 shows only the rear part of the rotorblade 1, which is adjacent to a rotor blade trailing edge 2. The twosides of the rotor blade 1, a suction or reduced-pressure side 4 whichis shown at the top in FIG. 1 and a pressure side 6 which is shown atthe underneath in FIG. 1, come together at the rotor blade trailing edge2. The two sides of the rotor blade 1 meet at an acute angle α. Theangle α is formed by a plane 8 which contains the substantially flatpressure side 6 of the rotor blade 1, and an inclined plane a. The planea contains a portion 4 a of the reduced-pressure side 4 of the rotorblade 1, the portion 4 a being directly adjacent to the rotor bladetrailing edge 2. The portion 4 a which is of a substantially flatconfiguration therefore determines in a region A the degree of taper ofthe rotor blade 1 towards the rotor blade trailing edge 2. A portion 4 bof the reduced-pressure side 4 adjoins the portion 4 a steplessly, thatis to say without forming a stair-like step. The portion 4 b is part ofa plane b which forms an angle β with the plane 8. The angle β issmaller than the angle α so that the portion 4 b of the reduced-pressureside 4 includes, with the pressure side 6, a more acute angle than isthe case between the portion 4 a and the plane 8. Therefore, in theregion B in FIG. 1, the degree of taper of the rotor blade 1 isdetermined by the gradient of the portion 4 b. The degree of taper inthe region B of the portion 4 b is smaller than in the region A of theportion 4 a. Within each of the respective regions B and A respectivelyhowever, the degree of taper is almost constant as the portions 4 b and4 a of the reduced pressure side 4 are, in themselves, substantiallyflat.

The portion 4 b is then in turn followed in a direction towards therotor blade leading edge (not shown) in a stepless configuration—in theabove-defined sense—by the next portion 4 c of the reduced-pressure side4, the portion 4 c also being in the form of an inclined plane. Theportion 4 c is part of a plane c which forms an angle γ with the plane8. The angle γ is in turn smaller than the angle β. The region C of therotor blade 1, the dimensions of which are determined by the length ofthe portion 4 c of the reduced-pressure side 4, also has an almostconstant degree of taper of the rotor blade 1, as the portion 4 c andthe pressure-side 6 disposed in opposite relationship in that region arealso substantially flat.

After the portion 4 c, as viewed from the rotor blade trailing edge 2,the portion 4 c is again steplessly adjoined by a portion 4 d. Theforegoing description relating to the portions 4 a to 4 c alsocorrespondingly applies to the portion 4 d. Depending on the respectiverequirements made on the rotor blade 1, the above-described successivearrangement of inclined planes within the reduced-pressure side 4, whichinclude increasingly more acute angles with the pressure side 6, can becontinued as desired. In a preferred embodiment, bends in thecross-section of the trailing edge portion 14 of the rotor blade, thatis to say a portion adjacent to the rotor blade trailing edge, areformed at the respective spacings, and between said bends said portionof the rotor blade is substantially flat. It should be emphasized inthis respect that the drawing shows the actual configurations andrelationships in greatly exaggerated form for the sake of enhancedclarity of the drawing.

FIG. 2 shows a view on an enlarged scale of a part as indicated at 10 inFIG. 1, for further clarification. It will be particularly clear fromFIG. 2 that there is no change in level in the form of a step betweenthe inclined plane 4 a and the inclined plane 4 b, but the portions 4 aand 4 b adjoin each other at a bend 12 in the reduced-pressure side 4.It will also be clear that the angle α between the portion 4 a and thepressure side 6 is greater than the angle β which is included betweenthe portion 4 b of the reduced-pressure side 4 and the pressure side 6.

What is claimed is:
 1. A wind power installation rotor blade having arotor blade trailing edge, wherein a cress section of the rotor bladetapers towards the rotor blade trailing edge, characterised in that thedegree of taper of the rotor blade increases in a direction towards therotor blade trailing edge in the region of the rotor blade trailingedge, the degree of taper increases at spacings and remains constantbetween the locations at which the increase occurs.
 2. A rotor bladeaccording to claim 1 characterised in that the degree of taper increasesin the form of at least one bend in the rotor blade.
 3. A rotor bladeaccording to claim 2 characterised in that the bend or bends extends orextend substantially parallel to the rotor blade trailing edge.
 4. Arotor blade according to claim 2 characterised in that there are threebends.
 5. A rotor blade according to claim 2 characterised in that thebend or bends is or are provided only on one side of the rotor blade. 6.A rotor blade according to claim 2 having a pressure side and areduced-pressure side, characterised in that the bend or bends is or areprovided only on the reduced-pressure side.
 7. A wind power installationhaving a rotor which has one or more rotor blades according to claim 1.8. A wind power installation rotor blade having a rotor blade trailingedge, wherein a cross section of the rotor blade tapers towards therotor blade trailing edge, characterised in that the degree of taper ofthe rotor blade increases in a direction towards the rotor bladetrailing edge in the region of the rotor blade trailing edge, the degreeof taper increases at spacings and remains constant between thelocations at which the increase occurs; and further comprising a rotorblade trailing edge portion of the rotor blade, which is adjacent to therotor blade trailing edge, characterised in that one side of the rotorblade trailing edge portion is substantially flat.
 9. A rotor bladeaccording to claim 8 characterised in that the substantially flat sideof the rotor blade trailing edge portion includes, with the other side,angles which are increasingly more acute in a direction towards therotor blade leading edge, as viewed from the rotor blade trailing edge.